When someone local (Boston area) says they saw a huge spider in a web, this is my first guess: cross orbweaver Araneus diadematus*. This spider has seemed more common in recent years, but that may be my impression since I've realized what they are. These are what across the pond they simply call "garden spiders." We also have garden spiders in eastern North America, but they are a different, larger, yellower species. In fact, it seems to me that I haven't seen a native garden spider in years, while I keep seeing more and more cross orbweavers. Not that native garden spiders are disappearing--friends and acquaintances post pictures of them regularly, usually terrified that something dangerous is in their yard. Neither garden spider is at all dangerous to humans of course.